As image recording methods for forming an image on a recording medium such as paper based on an image data signal, there are an electrophotographic system, sublimation type and melt type thermal transfer systems, an inkjet system, etc.
With regard to the inkjet system, the printing equipment is inexpensive, it is not necessary to use a plate when printing, and since an image is formed directly on a recording medium by discharging an ink composition only on a required image area, the ink composition can be used efficiently and the running cost is low, particularly in the case of small lot production. Furthermore, there is little noise and it is excellent as an image recording system, and has been attracting attention in recent years.
Among them, an inkjet recording ink composition (radiation-curing inkjet recording ink composition), which is curable upon exposure to radiation such as UV rays, is an excellent system from the viewpoint of it being possible to print on various types of recording media because, compared with a solvent-based ink composition, the drying properties are excellent and an image is resistant to spreading since the majority of the components in the ink composition cure upon exposure to radiation such as UV rays.
Various radiation curing ink compositions have previously been proposed; JP-A-2007-131755 (JP-A denotes a Japanese unexamined patent application publication) describes an actinic radiation curable ink for ink jet comprising a polymerizable monomer, the polymerizable monomer comprising a monofunctional monomer at 80 wt % to 99.99 wt % and a polyfunctional monomer at 20 wt % to 0.01 wt % relative to the entire monomer, and the percentage change of weight of a cured film of said ink when immersed in said ink for 30 seconds being no greater than 30 wt %.
Currently, when printing is carried out using an ink jet printer by firing ink droplets onto plain paper or a non-water absorbing recording medium such as a plastic, higher speed, higher image quality, and fixation onto the recording medium are important objects.
JP-A-2008-100501 discloses an ink set for ink jet recording for the purpose of improving image uniformity, etc. between various recording media, the ink set comprising at least a colored liquid composition comprising at least a polymerizable compound, a photopolymerization initiator, and a colorant and an undercoat liquid composition comprising at least a polymerizable compound and a photopolymerization initiator, the polymerizable compound contained in the colored liquid composition comprising at least one type of monofunctional monomer and at least one type of polyfunctional monomer, the amount of monofunctional monomer in the entire colored liquid composition being 10 to 70 wt %, and the amount of polyfunctional monomer being 10 to 50 wt %.
Furthermore, improving the durability, etc. of a printed material is also an object.
JP-A-2010-000788 discloses an ink jet printed material for the purpose of obtaining an ink jet printed material having excellent weatherability and durability, the ink jet printed material having a transparent protective layer formed on the surface, the ink jet printed material comprising a substrate and a picture layer formed above the substrate by ink jet type printing, the transparent protective layer being formed above the picture layer, the picture layer comprising a UV-curable resin ink that cures upon irradiation with UV, and the transparent protective layer comprising an electron beam-curable resin that cures upon irradiation with an electron beam.